2,837 research outputs found
Demonstration of negative group delays in a simple electronic circuit
We present a simple electronic circuit which produces negative group delays
for base-band pulses. When a band-limited pulse is applied as the input, a
forwarded pulse appears at the output. The negative group delays in lumped
systems share the same mechanism with the superluminal light propagation, which
is recently demonstrated in an absorption-free, anomalous dispersive medium
[Wang et al., Nature 406, 277 (2000)]. In this circuit, the advance time more
than twenty percent of the pulse width can easily be achieved. The time
constants, which can be in the order of seconds, is slow enough to be observed
with the naked eye by looking at the lamps driven by the pulses.Comment: 6pages,8 figure
Generation of photon pairs using polarization-dependent two-photon absorption
We propose a new method for generating photon pairs from coherent light using
polarization-dependent two-photon absorption. We study the photon statistics of
two orthogonally polarized modes by solving a master equation, and show that
when we prepare a coherent state in one polarization mode, photon pairs are
created in the other mode. The photon pairs have the same frequency as that of
the incident light.Comment: 4 pages, 3 figures, submitted to PR
Simulation of Slow Light with Electronics Circuits
We present an electronic circuit which simulates wave propagation in
dispersive media. The circuit is an array of phase shifter composed of
operational amplifiers and can be described with a discretized version of
one-dimensional wave equation for envelopes. The group velocity can be changed
both spatially and temporarily. It is used to emulate slow light or stopped
light, which has been realized in a medium with electromagnetically induced
transparency (EIT). The group-velocity control of optical pulses is expected to
be a useful tool in the field of quantum information and communication.Comment: The following article has been submitted to the American Journal of
Physics. After it is published, it will be found at
http://scitation.aip.org/ajp (7 pages, 7 figures
Absorption-free optical control of spin systems:the quantum Zeno effect in optical pumping
We show that atomic spin motion can be controlled by circularly polarized
light without light absorption in the strong pumping limit. In this limit, the
pumping light, which drives the empty spin state, destroys the Zeeman coherence
effectively and freezes the coherent transition via the quantum Zeno effect. It
is verified experimentally that the amount of light absorption decreases
asymptotically to zero as the incident light intensity is increased.Comment: 4 pages with 4 figure
Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures
We investigated macroscopic quantum tunneling (MQT) of
BiSrCaCuO intrinsic Josephson junctions (IJJs) with two device
structures. One is a nanometer-thick small mesa structure with only two or
three IJJs and the other is a stack of a few hundreds of IJJs on a narrow
bridge structure. Experimental results of switching current distribution for
the first switching events from zero-voltage state showed a good agreement with
the conventional theory for a single Josephson junction, indicating that a
crossover temperature from thermal activation to MQT regime for the former
device structure was as high as that for the latter device structure. Together
with the observation of multiphoton transitions between quantized energy levels
in MQT regime, these results strongly suggest that the observed MQT behavior is
intrinsic to a single IJJ in high- cuprates, independent of device
structures. The switching current distribution for the second switching events
from the first resistive state, which were carefully distinguished from the
first switchings, was also compared between two device structures. In spite of
the difference in the heat transfer environment, the second switching events
for both devices were found to show a similar temperature-independent behavior
up to a much higher temperature than the crossover temperature for the first
switching. We argue that it cannot be explained in terms of the self-heating
owing to dissipative currents after the first switching. As possible
candidates, the MQT process for the second switching and the effective increase
of electronic temperature due to quasiparticle injection are discussed.Comment: 10pages, 7figures, submitted to Phys. Rev.
Helical mode conversion using conical reflector
In a recent paper, Mansuripur et al. [Phys. Rev. A 84, 033813 (2011)]
indicated and numerically verified the generation of the helical wavefront of
optical beams using a conical-shape reflector. Because the optical reflection
is largely free from chromatic aberrations, the conical reflector has an
advantage of being able to manipulate the helical wavefront with broadband
light such as white light or short light pulses. In this study, we introduce
geometrical understanding of the function of the conical reflector using the
spatially-dependent geometric phase, or more specifically, the spin redirection
phase. We also present a theoretical analysis based on three-dimensional matrix
calculus and elucidate relationships of the spin, orbital, and total angular
momenta between input and output beams. These analyses are very useful when
designing other optical devices that utilize spatially-dependent spin
redirection phases. Moreover, we experimentally demonstrate the generation of
helical beams from an ordinary Gaussian beam using a metallic conical-shape
reflector.Comment: 7 pages, 7 figure
Observation of Brewster's effect for transverse-electric electromagnetic waves in metamaterials: Experiment and theory
We have experimentally realized Brewster's effect for transverse-electric
waves with metamaterials. In dielectric media, Brewster's no-reflection effect
arises only for transverse-magnetic waves. However, it has been theoretically
predicted that Brewster's effect arises for TE waves under the condition that
the relative permeability r is not equal to unity. We have designed an array of
split-ring resonators as a metamaterial with mu_r 1 using a finite-difference
time-domain method. The reflection measurements were carried out in a 3-GHz
region and the disappearance of reflected waves at a particular incident angle
was confirmed.Comment: 4 pages, 5 figure
Spectral-Function Sum Rules in Supersymmetry Breaking Models
The technique of Weinberg's spectral-function sum rule is a powerful tool for
a study of models in which global symmetry is dynamically broken. It enables us
to convert information on the short-distance behavior of a theory to relations
among physical quantities which appear in the low-energy picture of the theory.
We apply such technique to general supersymmetry breaking models to derive new
sum rules.Comment: 18 pages, 1 figur
Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC
In supersymmetric scenarios with a long-lived stau, the LHC experiments
provide us with a great environment for precise mass measurements of
superparticles. We study a case in which the mass differences between the
lightest stau and other sleptons are about 10 GeV or larger, so that the decay
products of heavier sleptons are hard enough to be detected. We demonstrate
that the masses of neutralinos, sleptons, and squarks can be measured with a
good accuracy.Comment: 20 pages, 6 figure
Naturalized and simplified gauge mediation
Following recent developments in model building we construct a simple,
natural and controllable model of gauge-mediated supersymmetry breaking.Comment: 8 pages, minor change
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